04 January 2010

A Force of Nature: Our Influential Anthropocene Period

'We live in epoch-making times. I mean this literally, rather than as a tool to dramatise the global economic crisis or latest political scandal. An epoch describes a geological time period. The end of the last glaciation, some 11,000 years ago, saw the transition from the cool Pleistocene to the warmer Holocene. This relatively stable epoch saw humans turn to agriculture and our population rise considerably. Now geologists, ecologists and climate scientists, myself included, are reporting we have entered a new and much less stable geological epoch: the Anthropocene.

Just as changes to the Earth's orbit, volcanic eruptions and asteroid impacts in the distant past have set the world on radically new courses, humanity itself has now become a collective force of nature, with far-reaching consequences. But what does this startling discovery – that humanity has become a globally significant geophysical force – mean for society, solving environmental problems, and perhaps more profoundly, how we see ourselves?

People have always had an impact on the environment. The difference now is that rather than influencing only local environments in limited ways, humanity is having planet-wide impacts on the Earth's workings. The best known global change is the rise in atmospheric carbon dioxide and resulting climatic changes. Some of the CO2 in the atmosphere dissolves into the oceans, making them more acid, which is degrading marine ecosystems. To put this in context, the oceans are more acidic today that they have been for at least 800 millenia. The atmospheric CO2 increase has also boosted plant growth in some places, changing the world's forests and grasslands. In short, the global cycling of carbon has been significantly altered.

The impacts of human activity on the other great global chemical cycles are similarly profound. To increase crop yields, more nitrogen is added to ecosystems through fertiliser use, than is added by all natural processes combined. But fertiliser run-off leads to 'dead-zones' of low-oxygen water that currently affect 245,000 sq km of the world's ocean.

Furthermore, scientists estimate that each year humans move more rock, sediment and soil than all natural processes , that at least three times as much fresh water is held in reservoirs than in rivers, and at least a third of all land has been appropriated for human use.

The heavy hand of humanity reaches into the living world too. Each year, we extract 7m tonnes of bushmeat from tropical forests, 95m tonnes of fish from the oceans, and raze 80,000 sq km of forest. The result: we are at the leading edge of the sixth mass extinction in Earth's history. Extinction rates today are at least 100 times higher than 'background' rates. Previous extinctions, such as that which wiped out the dinosaurs 65m years ago, are joined by a human-induced loss of life.

Many of these trends look set to continue or accelerate, with potentially dire consequences. Recent events may provide a taste of what's to come: in 2007 and 2008 food protests erupted across three continents, in part because of the switch of some land from food to biofuel production. In the same period, about 1% of humanity had their homes damaged or destroyed by extreme weather events. Interlinked feedback loops amongst political, economic and environmental spheres could lead to grave problems without foresight and planning.

The big question in the Anthropocene is: can we learn to manage our own global life-support system and avoid crossing dangerous thresholds? The answer so far, if progress in 14 years of UN climate change talks is a measure, is probably no.

But perhaps there are grounds for cautious optimism. The word "Anthropocene", coined by Nobel prize winner Paul Crutzen, has greatly assisted researchers in understanding how the Earth and human society function together. Perhaps pushing the concept into wider usage would enable politicians, business leaders, social movements and NGO's to similarly benefit from thinking along integrated, quantitative and evidence-based lines.

Of course, scientific knowledge itself cannot set goals for society. Choosing how to manage our life support system is within the realm of politics. Scientists can identify the likely (and unlikely) outcomes of choices we face. For instance, humanity's impact on the environment has been greatest over the last 50 years. In this time human numbers have doubled and the global economy increased more than fifteen-fold. Our socio-economic system and the fossil fuels that power it lie at the heart of understanding how humans have become a force of nature, and therefore how to alter our future impacts.

Big ideas from science are often discomfiting. The Anthropocene is no exception. There is a temptation to see humanity as "bad" for despoiling the environment, or to deny the evidence through fear of acknowledging the need for profound changes. I see it as an update on how we view our place in the universe. First, Copernicus discovered that the Earth revolves around the sun, and humanity is not at the centre of the universe. Then, Darwin established that we are not even at the heart of life on Earth. Now Crutzen has reversed this trend by naming a new human-dominated geological epoch...'

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